Recently, prevention and the like of locomotive syndrome and sarcopenia (reductions in muscle quantity and muscle strength, and decrease in physical function) attract attentions, and it is demanded to ameliorate such symptoms by increases in muscle quantity and muscle strength. Also for healthy persons, prevention of muscular fatigue and enhancement of muscle are demanded.
In an initial process of muscle cell differentiation, an undifferentiated cell differentiates into a myoblast which is a cell derived from a muscle fiber. The myoblast further differentiates, and a protein that is specific to a muscle cell is expressed. A phenomenon characteristic of differentiation of a muscle cell is cell fusion, i.e., a phenomenon that myoblasts which are mononuclear cells fuse to differentiate into a myotube cell which is a multinucleate cell. Further, through a process of formation of a muscle fiber having a contracting ability from a matured myotube cell, muscle is completed. During the differentiation of myoblasts, characteristic proteins such as tropomyosin and myosin heavy chain are generated, and these are used as differentiation markers (Non-Patent Literature 1).
Peptide molecules are known to have various pharmacological effects. For example, Patent Literature 1 describes that dipeptides such as Hyp-Gly have an osteoclast differentiation inhibiting effect, an alkaline phosphatase inhibiting effect, and so on. Non-Patent Literature 2 describes that peptides such as Hyp-Gly-Pro have an antioxidative effect. Patent Literature 2 describes that peptides such as Pro-Gly and Hyp-Gly which further have up to ten amino acids in their upstream region and/or in their downstream region, have effects of stimulating growth, maintenance and repair of bone or the like.
Patent Literature 3 describes that Rosa roxburghii, a soybean peptide, a C12 peptide and the like have a myoblast activating effect. However, whether these peptide molecules have a myoblast differentiation promoting effect has not been known.
Non-Patent Literature 3 shows the rate of change in muscle weight when American football players took in an equivalent mixture of a collagen peptide and a whey peptide for three months in combination with exercise. Although the muscle weight increased (FIG. 2), the body weight also increased (FIG. 1) after intake of this equivalent mixture, and the muscle, in terms of a ratio of the muscle weight to the body weight, was rather reduced in comparison with the starting point. In contrast to this, in the present invention, the ratio of the muscle weight to the body weight significantly increases as described in later-described Test Example 2.